This invention relates to a coupler for precisely positioning the endface of an optical waveguide filament with respect to an optoelectronic device.
Optical waveguide filaments are a promising transmission medium recently developed for use in optical communication systems. Such filaments generally consist of a transparent core surrounded by a layer of transparent cladding material having a refractive index lower than that of the core. It has been well known in the art that light can be propagated along a transparent fiber structure having a higher refractive index than its surroundings. The small difference between core and cladding refractive indices in optical waveguides results in an acceptance angle that is smaller than that of conventional optical fibers, the numerical aperture of optical waveguides generally being about 0.2. Moreover, the fact that a single optical waveguide can be utilized to transmit one or more signals necessitates the coupling of at least one discrete light beam to a single waveguide filament. Thus, suitable means must be provided for efficiently coupling an optical source to such optical waveguide filaments.
The light emission from an optical waveguide source must be highly directional in order to efficiently couple to the optical waveguide because of its low acceptance angle. Since only a very bright light source having the described characteristics can yield efficient coupling, lasers and laser diodes are usually considered for this role. It is necessary to precisely position the endface of an optical waveguide filament with respect to such a light source since a narrow beam of light is emitted from a small area thereof. Likewise, efficient, low-noise, high bandwidth detectors may have small active or sensitive areas.